在Objective-C中测试nil-if(x！= nil)vs if(x) [英] Testing for nil in Objective-C -- if(x != nil) vs if(x)

问题描述

我在网上找到的大多数示例都这样写:

Most of the examples I found on the net write this:

if(x != nil)
    // ...

这有什么问题吗?

if(x)
    // ...

我在一个简单的程序中都尝试过，但没有发现任何区别.

I tried both in a simple program and couldn't found any difference.

推荐答案

在Objective-C中，nil定义为名为__DARWIN_NULL的值，其在if语句中的值实际上为0或false .因此，写作 if (x == nil)与写if (!x)相同，写if (x != nil)等于if (x)(因为与false比较会产生否定，与true进行比较会保持相同的条件).

In Objective-C, nil is defined as a value called __DARWIN_NULL, which essentially evaluates to 0 or false in if-statements. Therefore, writing if (x == nil) is the same as writing if (!x) and writing if (x != nil) is equal to if (x) (since comparing to false creates a negation, and comparing to true keeps the condition the same).

您可以以任何一种方式编写代码，而这实际上取决于您认为可读性更高的代码.我发现if (x)更有意义，但这取决于您的风格.

You can write your code either way, and it really depends on which you think is more readable. I find if (x) to make more sense, but it depends on your style.

这就像比较if (someCondition == true)与if (someCondition).
这一切都取决于您，以及谁来读取代码.

It's like comparing if (someCondition == true) versus if (someCondition).
It all depends on you, and who's going to be reading the code.

正如Yuji正确提到的那样，由于Objective-C是C的超集，因此任何求值为0以外的值的条件都被认为是真实的，因此，如果someCondition在上面的示例中，计算结果为整数值-1，将其与true进行比较将得出false，并且不会评估if语句.要注意的事情.

As Yuji correctly mentions, since Objective-C is a superset of C, any condition that evaluates to a value other than 0 is considered to be true, and therefore, if someCondition in the example above were to evaluate to an integer value of, say, -1, comparing it to true would result in false, and the if-statement would not be evaluated. Something to be aware of.

这篇关于在Objective-C中测试nil-if(x！= nil)vs if(x)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！